The present invention relates to an information recording/reproducing apparatus and, more particularly to an information reproducing apparatus which records an audio still-picture program on a predetermined recording medium.
Audio still-picture programs having highly precise still pictures and various display effects for updating the still picture of interest (by cutting, scrolling, wiping, dissolving, etc.) rather than merely changing over the screen can be provided in the form of digital data as one or are packet transmitted through a communication satellite channel or CATV.
In the case of a still-picture program, an audio still-picture program, in particular, digital data representing sound and image are sent in the form of packet type data. The format of this packet is shown in FIG. 3.
As shown in FIG. 3, one frame (=2048 bits) includes 7 packets. The leading 16 bits of this frame are used for a synchronizing signal FS. Another 16 bits are further attached to the synchronizing signal FS as a frame control signal FC. The frame control signal FC contains additional information such as mode information.
Furthermore, one packet (288 bits) is comprised of 16-bit headers HA and HS, 174-bit data portion, and 82-bit error correction data. The header HA indicates an attribute of the packet, that is, a kind of service (i.e. whether the packet is an audio still-picture program). The header HS is information indicating a kind of packet in the attribute indicated by the header HA. If the header HS is examined, it can be determined whether information in the data portion located immediately after the header HS is program control data. In the case of an audio still-picture program, if the header HS is examined, it can be determined whether the data which is located immediately after the header HS is on sound or image. The 174-bit data portion contains audio data, image data, and program control data. Program control data are information indicating the start or end of the program, transmission time, display time, and the like.
The digital still-picture program is transmitted at the transmission speed of several Mbps, and audio data and image data are both compressed.
In the image compression, each screen is coded one by one, and packets including additional information such as a synchronizing signal, coding parameter, and coding data are transmitted according to the coding format. The audio data is coded in every several ms, and transmitted as a packet having a synchronizing signal, coding parameter, coding data, and the like. However, the synchronizing signal of the coding format of the image data and that of the audio data are not simultaneously transmitted.
FIG. 2 shows the apparatus which records, reproduces, and searches an audio still-picture program transmitted in the above-described packets.
In the recording, a digital data string inputted from the input terminal 100 is synchronized by the synchronizing signal FS in the reception/demodulation circuit 102. The string is received and demodulated in this circuit 102. The demodulated digital data is separated into each packet by the packet separating circuit 104. The header correcting circuit 106 decodes the error correcting codes of the headers HA and HS. The error correcting decoder 108 decodes the error correcting codes which are attached to the header HS and the data portion.
In the packet string in which the error correcting code is decoded in the error correcting decoder 108, a kind of service is identified by the service identification circuit 110 in accordance with the header HA, and the packets of the audio still-picture program are picked up. Then, in the searching information adding circuit 112, information needed for search is added, and the information is transmitted to the recording reproducing circuit 118 through the bus A. This recording reproducing circuit 118 receives a recording control signal from the recording reproduction search control circuit 116 and writes in the recording medium 120 (i.e. magneto-optic disk). The above-described recording processings are controlled by CPU 122.
In the reproduction and search, under the control of the CPU 122, the recording reproducing circuit 118 receives a reproduction control signal from the recording reproduction search control circuit 116 and reads out the data from the recording medium 120. Furthermore, the circuit 118 decodes the error correcting code and transmits the data to the bus A. The searching information read-out circuit 126 reads out necessary information for search through the bus A. The CPU 122 controls search and reproduction on the basis of this searching information.
The packet string which is read out under the control of the CPU 122 on the basis of the searching information is identified whether it is on audio data or image data by the packet identification circuit 126. Then, the packet of audio data is transmitted to the audio decoder 136 and the packet of image data is transmitted to the image decoder 138.
The audio decoder 136 decodes the audio packet and outputs it through the output terminal 140 as audio data. The image decoder 138 decodes the image packet and calculates the timing of image display from the transmitted transmission time data and image display time data. When the time for displaying the image has come, the decoded image packet is outputted from the output terminal 142 as an image signal.
After that, an audio amplifier, speaker, and monitor (not shown) connected to the output terminals 140 and 142 reproduce the audio still-picture program.
However, in the above-described prior art, problems have arisen in the case where a still-picture program or audio still-picture program is recorded or an image is searched for and the program is reproduced from that searching point. This problem is described below in detail.
Generally, in the case of the still-picture program or audio still-picture broadcasting, program control data includes an image transmission time (a reception time) and broadcasting time (an actual time when an image is displayed). In this type of apparatus, demodulated image data is displayed at a specified time according to a designated display switch effect. In the audio reproduction, a received sound is demodulated and reproduced at real time.
That is, the image data is received and stored in a memory in advance and displayed at a specified time. On the other hand, the audio data is reproduced at real time. In other words, the audio data is received much later than the corresponding image data.
There is no problem under such a condition in the case where a still-picture program or audio still-picture data is received and merely outputted. However, the problem has arisen in the case where the image data and audio data are recorded on a magneto-optic disk and the like, and reproduced at an operator's desired time (the designated broadcasting time might have already passed).
As described above, in the case of a still-picture program and an audio still-picture program, an image being displayed on a monitor is not the image being received at real time, but received earlier than the monitor display. Therefore, when a program recording on the recording medium 120 is started, the actual recording is started from the image which is displayed much later. In other words, the still picture which is being displayed at the point where the operator has designated for recording cannot be actually recorded. Furthermore, in the case of a still-picture program (including an audio still-picture program), since a still picture which is displayed on a screen is delivered as a plurality of packets, if the recording on the recording medium 120 is started with the packet which is received after the operator has designated a recording, the recording is started with the packet which is in the middle of a packet group comprising a still picture. If the program recorded in that way is reproduced, the first image cannot be reproduced correctly since the signal of the first image cannot be synchronized. For the above-described reasons, in the case where the still-picture program is recorded, the recording needs to be started at the head of the packets of the still-picture program.
To record the still-picture program from the beginning to the end on the recording medium 120, the recording needs to be started much earlier than the display time. However, there is the other drawback that an unnecessary part of a program may also be recorded.
The problem may arise when the audio still-picture program recorded in the recording medium 120 is reproduced. The reasons will be described along with FIG. 4. In the diagram, Vk (k=1, 2, . . . ) represents an image packet and AL (L=1, 2, 3, . . . ) represents an audio packet. The diagram illustrates the state that the packets are stored in the order of reception.
It is assumed that the image packets are read out from the point A. When the image packets V1, V2, and V3 are read out, the audio packets A1, A2, A3, . . . which are located after the point B are read out. However, the audio packets A1, A2, A3, . . . are simply transmitted later than the image packets V1, V2, V3 timewise. It is not always that the audio packets A1, A2, A3 correspond to the image packets V1, V2, V3. In the case of the audio data, normally, the first packet of a series of audio data includes a synchronizing signal which commands the starting of an audio reproduction. However, in the case where the audio packet A1 does not contain a synchronizing signal, there is the problem that the demodulation processing can not be correctly performed resulting in noise generation.